Understand the natural mechanics behind a rainbow and the green clouds will begin to make sense. Lovely color.

Very interesting: thanks!

Perhaps green clouds are more common than I realize: I did not see these when I took the shot, or during casual inspection of images soon after. Only yesterday when I started processing and paying attention to the mountain shadow did I notice the cloud colour.

Maybe a little too much shadow but it's still a very interesting photograph.

Thanks Ian! I think the shadows had to be that dark to bring out the colours. I'll take another look at it.

I'm afraid that, like Ian, I don't entirely get the rainbow and diffraction explanation. The light is diffracting through a narrow opening? Why is the green so widespread, the red so narrow, and the other parts of the spectrum missing?